IntroductionFrom fortified borders to decorative garden walls, fences form ubiquitous widespread networks that sprawl across the global terrestrial landscape. Fences and walls are one of the oldest tools used by people to manage other people and wildlife, e.g., by marking territorial boundaries, separating livestock from wild animals, or monitoring the movement of people through border controls. There is no reliable measure of extent of the global fence network, however it is estimated to be at least 10 times that of the global road network (Jakes et al. 2018), which is currently more than 64 million km (Dulac 2013), and expected to reach 90 million km by 2050 (Laurance et al. 2014). Despite the enormous extent of the fence network, fences are rarely subjected to Environmental Impact Assessments, and the ecological impacts of fencing are severely underestimated and understudied (Jakes et al. 2018, McInturff et al. 2020, Buton et al. 2024). The main purposes of a fence – to fragment, isolate and/or reduce interactions – often align with negative ecological impacts, while meeting the goals to protect livestock, prevent access of invasive species, and control the spread of diseases (Terborgh et al. 2001, Woodroffe et al. 2014, Jakes et al. 2018, Mysterud and Rolandsen 2019, McInturff et al. 2020). Fences and walls are erected through all landscapes, including those that are ecologically important and protected. One example that has received a lot of media and political attention, is the recently constructed border fence between Poland and Belarus which cuts through Białowieża Forest, the best preserved lowland temperate forest in Europe and transboundary World Heritage Site (Jaroszewicz et al. 2021). Such barriers have the goal to hinder the flow of people, and consequently also block the movement of wildlife and challenge landscape connectivity (Olson and van der Ree 2015, Linnell et al. 2016), which can trigger a cascade of direct and indirect ecological impacts (e.g. Nowak et al, submitted). Border fences are also used to control the spread of diseases, such as African Swine Fever (ASF). With the aim to reduce the movement of infected wild boar, and contain ASF, fences have been built along numerous country borders in Europe, e.g., the 70-km long ASF fence at the German-Danish border which runs directly through Natura 2000 areas (Eilenberg and Harrisson 2023, Klein et al. 2024). Similar border fences to control ASF exist at the German-Polish border, and are planned to be installed at the Norwegian-Swedish border. The fragmentation effect of border fences is clear and apparent, however the impacts caused by fences that are for example, along roads and railways, denote property borders, or enclose protected areas are often underestimated. Without proper research of the downstream or indirect impacts to non-target species and the functioning of ecosystems, negative impacts of fences will continue to be overlooked and unaccounted for. This special issue provides a collection of articles in which authors present different perspectives on fences and how we, as humans, use fences to communicate with the natural world and manage wildlife. Finally, the issue provides guidelines to improve fence design and implementation, and discusses research steps to move forward in the field.